The Salmonella type III secretion translocon protein SspC is inserted intothe epithelial cell plasma membrane upon infection

Salmonella species translocate effector proteins into the host cell cytopla sm using a type III secretion system (TTSS). The translocation machinery pr obably contacts the eukaryotic cell plasma membrane to effect protein trans fer. Data presented here demonstrate that both SspB and SspC, components of the translocation apparatus, are inserted into the epithelial cell plasma membrane 15 min after Salmonella typhimurium infection. In addition, a yeas t two-hybrid interaction between SspC and an eukaryotic intermediate filame nt protein was identified. Three individual carboxyl-terminal point mutatio ns within SspC that disrupt the yeast two-hybrid interaction were isolated. Strains expressing the mutant SspC alleles were defective for invasion, tr anslocation of effector molecules and membrane localization of SspC. These data indicate that insertion of SspC into the plasma membrane of target cel ls is required for invasion and effector molecule translocation and that th e carboxyl terminus of SspC is essential for these functions.